In a microorganism, L-valine, one of branched-chain amino acids, is biosynthesized starting from pyruvate via acetolactic acid, dihydroxy isovaleric acid, and ketoisovaleric acid. These intermediate metabolic products are produced by a reaction catalyzed by acetohydroxy acid synthase, actohydroxy acid isomeroreductase, dihydroxy acid dehydratase, and transaminase B. However, these enzymes also involve in L-isoleucine biosynthesis starting from ketobytyric acid and pyruvate, and also L-leucine is biosynthesized from ketoisovaleric acid, which is an intermediate metabolic product, via 2-isopropylmalic acid, 3-isopropylmalic acid, and ketoisocaproic acid. Thus, since branched-chain amino acids, i.e. L-valine, L-isoleucine, and L-leucine use same enzymes for their biosynthesis processes, it is known that industrially producing one type of a branched-chain amino acid through fermentation has a difficulty. Moreover, there is a problem that industrial mass production is limited by feedback inhibition caused by L-valine, which is a final product, or a derivative thereof.
After a great deal of effort to develop a strain having enhanced L-valine productivity, the present inventors have completed the present invention by finding that a strain transformed to have an inactivated regulatory region of L-valine operon has superior L-valine productivity to a mother strain.